Method and device for controlling an internal combustion engine

Abstract

A method for injecting gaseous fuel directly into a combustion chamber of an internal combustion engine in order to heat a catalytic converter, the method including: carrying out a main injection of gaseous fuel directly into the combustion chamber; carrying out a first post-injection following the main injection but prior to an ignition, and following the ignition and preferably following the end of combustion in the combustion chamber, carrying out a second post-injection of gaseous fuel into the combustion chamber.

Description

FIELD[0001]The present invention relates to a method for injecting gaseous fuel directly into a combustion chamber of an internal combustion engine in order to heat a downstream catalytic converter; the present invention also relates to a control unit for executing the method.BACKGROUND INFORMATION[0002]In addition to liquid fuels, gaseous fuels are also increasingly used as fuels in internal combustion engines in the more recent past. In comparison with gasoline-operated internal combustion engines, gas-operated internal combustion engines, using natural gas or autogas, for example, are an attractive alternative for realizing savings potentials and reducing a CO2 emission. In addition, potentials with regard to reduced emissions are also obtainable. In an effort to achieve better efficiency, more attempts are also made to realize a direct injection of gas, where the gaseous fuel is injected directly into a combustion chamber of an internal combustion engine. An issue with gaseous f...

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Benefits of technology

[0003]An example method according to the present invention for the injection of gaseous fuel directly into a combustion chamber of an internal combustion engine in order to heat a catalytic converter may have the advantage of allowing rapid and effective heating of a catalytic converter having a temperature below a predefined threshold temperature. As a result, exhaust-gas emissions during a cold start are able to be significantly reduced. In addition, the method according to the present invention allows for considerably smoother running of the internal combustion engine, which provides clear advantages for a user, especially in the idling operation. According to the present invention, this may be achieved, for example, in that the method, in a first step, executes a main injection of gaseous fuel directly into the combustion chamber of the internal combustion engine. This is followed by a first post-injection after the main injection, in which a fuel quantity of the first post-injection is preferably considerably smaller than the fuel quantity injected during the main injection. The first post-injection takes place prior to an ignition in the combustion chamber. According to the present invention, a second post-injection of gaseous fuel into the combustion chamber is carried out following the ignition and following the end of the combustion in the combustion chamber. The fuel quantity of the second post-injection is likewise considerably smaller than that of the main injection. With the aid of the second post-injection, another combustion following the actual main combustion is able to be realized, thereby significantly increasing an exhaust-gas temperature. The catalytic converter, which is connected downstream from the combustion chamber, can therefore heat up more quickly, so that the emissions of the internal combustion engine in a cold start are able to be significantly reduced also in a direct injection. Because in the case of compressed natural gas (CNG), for example, an efficient exhaust-gas purification requires a catalytic-converter temperature of approximately 420° C., which is approximately 120 Kelvin higher than in the case of gasoline, the exhaust-gas temperature should be as high as possible. Of course, attention should be paid to keep the raw emissions of uncombusted hydrocarbons and particles as low as possible because they would otherwise clearly worsen the emission behavior in a catalytic converter that is still not functioning due to insufficient temperatures. The first post-injection generates additional turbulence around the spark plug and thereby enriches the fuel-air mixture with fuel in this region shortly before the ignition. This facilitates a flame development, and the flame core formation, and thus a subsequent combustion, are stabilized.

[0005]The second post-injection is preferably carried out when a discharge valve on the combustion chamber is opened. An onset of the second post-injection and an onset of the opening of the discharge valve especially preferably take place at the same time. This allows for the generation of an intensive charge movement in the combustion chamber in the direction of the discharge valve. In conjunction with the high charge temperature in the combustion chamber, this facilitates the oxidation of the quantity of gaseous fuel introduced with the aid of the second post-injection. The additional conversion generates a higher temperature of the exhaust-mass flow, and thus its enthalpy, which is utilized for more rapid heating of the catalytic converter after a start of the internal combustion engine. The second post-injection and the opening of the discharge valve preferably take place simultaneously.

[0006]It is especially preferred if the second post-injection starts directly after the combustion in the combustion chamber has been concluded. At this moment, the temperatures in the combustion chamber are at their peak so that an immediate ignition of the fuel introduced by the second post-injection is possible. Here, it is also avoided that the second post-injection takes place directly into a flame in the combustion chamber, which would drastically increase the number of particles and the emissions.

[0007]It is furthermore preferred if the first post-injection and the second post-injection are of equal length. In addition, equal volumes of fuel and, in particular, equal quantities of gaseous fuel are preferably injected during the first post-injection and the second post-injection. This allows for a particularly uncomplicated control of the method.

[0008]According to another preferred further development of the present invention, the combustion process is carried out as a lean process. In particular, the combustion process is carried out using a lambda value of lambda of approximately 1.05. This makes it possible to minimize the raw NOx emissions, in particular.

[0012]According to the present invention, a post-injection is thus carried out, preferably following the end of combustion, in order to increase an exhaust-gas enthalpy. An ignition of the post-injected gaseous fuel takes place in the combustion chamber due to the still prevailing high temperatures. The present invention may therefore also be used if a gas pressure is reduced, for instance on account of a relatively low gas tank level, because the pressure is low when the discharge valve opens following the combustion, so that a post-injection is nevertheless possible.

Problems solved by technology

An issue with gaseous fuels, especially natural gas, in comparison with gasoline or other liquid fuels is an exhaust-gas treatment.

In particular if the gaseous fuel has methane (CH4) as the main component, an exhaust-gas treatment becomes more complex than in the case or longer-chained hydrocarbons of liquid fuels.

A sufficient exhaust-gas treatment cannot be ensured in the case of cold catalytic converters, in particular.

Of course, attention should be paid to keep the raw emissions of uncombusted hydrocarbons and particles as low as possible because they would otherwise clearly worsen the emission behavior in a catalytic converter that is still not functioning due to insufficient temperatures.

This allows for a particularly uncomplicated control of the method.

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